Stringent health requirements govern the legal operation of evaporative air conditioners to ensure that public health standards are not violated. One requirement is a minimum three monthly cleaning of the drainage system. However, it is found in practice, particularly in hot climates and when the air conditioner is not in frequent use, significant microorganism populations can still grow in the water reservoir of the air conditioner in the period between cleaning.
In order to address this problem, and the general problem of having the base of the air conditioner permanently wet which leads to corrosion and other deterioration of the system, dump valves of various construction have been proposed to be incorporated in the water reservoir. Such dump valves are typically designed to release the water from the reservoir at regular intervals or when the air conditioner is turned off. Unfortunately however, there are problems associated with these dump valves which means that they do not fully meet the requirements for which they were designed. For instance, a common problem is that they are fitted to a typical waste outlet having a rim which prevents the last few milliliters of water from draining from the reservoir. Such a small quantity of water having a large surface area, is an ideal growth medium for microorganisms. Another problem is due to the manner in which the dump valve operates. Usually, operation is controlled by a 240 volt power source--which can be dangerous for maintenance personnel due to the presence of water--which closes off the outlet after the air conditioner has been turned off and the reservoir has been drained, thereby preventing the escape of any latent excess water draining into the reservoir or the draining of water which collects in the reservoir when it rains.